Concrete structures such as bridges and viaducts (hereafter, simply referred to as “structures”) not only deteriorate by themselves but also are affected by a weather variation, change in the ground, and load bearing over a course of a long period of time. These effects are accumulated, and at the time when an adverse condition occurs in addition to the accumulated effects, partial breakage or exfoliation will occur in the structure, possibly even causing an accident or damage to a third party. In order to prevent the structure from flaking, the structure must be constantly inspected and monitored.
One of methods of inspecting and monitoring a structure now under research is an infrared-ray inspection method which is capable of performing a wide range investigation highly efficiently without accessing to the structure. The infrared-ray inspection method is a method in which surface temperatures of a structure are measured with an IR camera and discrimination is made between damaged regions and non-defective regions having no damages based on the temperature differences. An IR thermal image analyzer is used in the infrared-ray inspection method.
FIG. 18 shows a basic configuration of an IR thermal image analyzer.
An IR camera 91 detects infrared ray energy emitted from an object to be measured 94 such as a structure, and takes an IR thermal image indicating temperature distribution on the surface of the object to be measured 94 by converting the detected infrared ray energy into a temperature. A display device 93 displays the IR thermal image taken by the IR camera 91.
If the object to be measured 94 has, in the inside thereof, a damaged region such as a cavity, crack or sand streak, the surface temperature of the damaged region becomes higher than the surface temperature of a non-defective region when the ambient temperature rises in daytime, for example. Therefore, if a local high-temperature region is found in the IR thermal image of the object to be measured 94 taken by the IR camera 91, it can be estimated that a damage is present in that region.